• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7A
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• pp.682-687
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• 2010

The IEEE 802.15.4a specification targets the low-rate (LR) Impulse-radio (IR) ultra-wideband (UWB) system which is now widely applied in the WPANs considering rather short distance communications with low complexity and power consumption. The physical (PHY) layer uses concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM), and direct sequence spreading with time hopping in order that both coherent and non-coherent receiver architectures are supported. In this paper, the performances of multiple access schemes compliant with IEEE 802.15.4a specification are investigated with energy detection receiver, which allow avoiding the complex channel estimation needed by a coherent receiver. However, the performance of energy detection receiver is severely degraded by multi-user interference (MUI), which largely diminishes one of the most fascinating advantages of UWB, namely robustness to MUI as well as the possibility to allow parallel transmissions. So as to improve the performance of multiple access schemes, we propose to apply the novel TH sequences as well as to increase the number of TH positions. The simulation results show that our novel multiple access schemes significantly improve the performance against MUI.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.4
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• pp.64-69
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• 2009

Bit-interleaved coded modulation(BICM) applied to Alamouti's orthogonal space-time block code(OSIBC) has a rate loss problem In this paper, we expand orthogonal space-time block code(OSTBC) and apply bit-interleaved coded modulation (BICM) to expanded OSTBC(XOSIBC) to obtain a diversity gain without a rate loss. Binary phase shift keying(BPSK) design example is presented. Simulation results are also provided.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.384-388
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• 2003

In this paper, we have proposed a OFDM/QPSK-DMR(Orthogonal frequency Division Multiplexing/Quadrature Phase Shift Keying Modulation-Digital Microwave Radio)system using BL-PSF(Band-limited pulse shaping filter) over the Microwave channel. In the proposed DMR system, STS-1(51.84 Mbps) of SONET(Synchronous Optical NETwork) is first modulated by OFDM/QPSK symbol and used Band-limited pulse shaping filter. The advantage of the proposed DMR system is to simplify system complexity and increase IFFT/FFT block use-efficiency. The system performance of single carrier and OFDM systems is already proved that those of DMR systems have the same performance over AWGN(Additive White Gaussian Noise) channel environment. Therefore, the system is analyzed between proposed OFDM/QPSK-DMR and single carrier DMR systems and simulated by BER performance and Signature curve over Microwave channel environment. Simulation result is that the proposed system performances are approaching to the performance of single carrier DMR system as the number of Sub-carriers increasing.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.817-826
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• 2001

In this paper, we implemented QPSK(Quadrature Phase-Shift Keying) modem which is widely used for communication systems, using a general Digital Signal Processor(DSP), TM320C31. Up to now, almost all of communication systems consist of hardware. However, the implemented system herein is composed of software and hardware part. Software part includes the modulation process, before passing D/A(Digital-to-Analog Converter) and the demodulation process, after passing A/D(Analog-to-Digital Converter) in IF(Intermediate Frequency) node. Hardware part is related to input, output and process of signal. To demonstrate the successful implementation of modem, the output results obtained from DSP processor are compared with the simulated result on the personal computer.

• Journal of information and communication convergence engineering
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• v.4 no.2
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• pp.71-74
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• 2006

A basic access method about IEEE 802.11 MAC layer protocol using IEEE 802.11 wireless LANs is the DCF thatis based on the CSMA/CA. But, cause of IEEE 802.11 MAC layer uses original backoff algorithm (exponential backoff method), when collision occurred, the size of contention windows increases the double size Also, a time of packet transmission delay increases and efficienty is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs a proposed enhanced backoff algorithm. It is considered the transmission time of transmission control protocol (TCP) packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (A WGN) and Rician fading channel. From the results, a proposed enhanced backoff algorithm produces a better performance improvement than an original backoff in wireless LAN environment. Also, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between packet size and the transmission time, allowing for an inference of the optimal packet size in the TCP layer.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.296-299
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• 2003

In this paper, an underwater acoustic digital transceiver is designed and implemented by a multiple DSPs system. We have designed a QPSK transmitter based on look-up table and 13-symbols Barker code is used for frame synchronization. Channel distortions are compensated by a wide-band beamformer based on FIR filter and an adaptive equalize. with RLS algorithm. Uniform linear array (ULA) with four elements is used for the spartial signal processing. 1/2 convolutional code and Viterbi decoder are implemented to overcome time-varying multi-path fading. Also, we show experimental results in the underwater anechoic basin at KRISO/KORDl and Goseong, Donghae and Soyang lake of Kangwon-do.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5A
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• pp.668-673
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• 2000

In this paper, not only the problems which could not be solved with Conventional Importance Sampling and Improved Importance Sampling of the early simulation method, and but also the improvements obtained in terms of computer run-time were studied, by applying the central moment algorithm to the digital communication channels. That is, the channel performance evaluation is done for obtaining the cumulative probability function of the statistical characteristics of received signal with estimating the central moment of the received signal mixed the noise in the digital communication receiver. We confirm the simulation run-time after we implemented the quaternary phase shift keying(QPSK) satellite communication channels using the Signal Processing Worksystem(SPW) of the Cadence incorporation to verify the suggested algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.553-564
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• 2000

In this thesis, mobile communication channel with multi-path fading which is major factor of performance degradation of DS-CDMA system has been considered. An MRC diversity and error correcting coding technique have been used to improve performance of MFSK-MDPSK/DS-CDMA system. The MFSK-MDPSK/DS-CDMA system performance has been obtained quantitatively by the numerical analysis. the modulations under consideration are noncoherent M-ary frequency shift keying(MFSK) and an MFSK based joint frequency phase modulation utilizing MFSK/DS-CDMA and MDPSK-DS-CDMA systems the MFSK-MDPSK/DS-CDMA system obtain a better performance . Also, the error performance of MFSK-MDPSK/DS-CDMA system in Nakagami fading environments is improved by increasing the number of diversity branch and coding gain.

• Journal of Communications and Networks
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• v.15 no.3
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• pp.276-282
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• 2013

Self-encoded spread spectrum (SESS) is a novel modulation technique that acquires its spreading code from a random information source, rather than using the traditional pseudo-random noise (PN) codes. In this paper, we present our study of the SESS system performance under pulsed-noise jamming and show that iterative detection can significantly improve the bit error rate (BER) performance. The jamming performance of the SESS with correlation detection is verified to be similar to that of the conventional direct sequence spread spectrum (DSSS) system. On the other hand, the time diversity detection of the SESS can completely mitigate the effect of jamming by exploiting the inherent temporal diversity of the SESS system. Furthermore, iterative detection with multiple iterations can not only eliminate the jamming completely but also achieve a gain of approximately 1 dB at $10^{-3}$ BER as compared with the binary phase shift keying (BPSK) system under additive white gaussian noise (AWGN) by effectively combining the correlation and time diversity detections.

• Journal of Communications and Networks
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• v.15 no.3
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• pp.283-291
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• 2013

In this paper, we propose new multiuser detectors (MUDs) based on compressed sensing approaches for the large-scale multiple antenna systems equipped with dozens of low-power antennas. We consider the scenarios where the number of receiver antennas is smaller than the total number of users, but the number of active users is relatively small. This prior information motivates sparsity-embracing MUDs such as sparsity-embracing linear/nonlinear MUDs where the detection of active users and their symbol detection are employed. In addition, sparsity-embracing MUDs with maximum a posteriori probability criterion (MAP-MUDs) are presented. They jointly detect active users and their symbols by exploiting the probability of user activity, and it can be solved efficiently by introducing convex relaxing senses. Furthermore, it is shown that sparsity-embracing MUDs exploiting common users' activity across multiple symbols, i.e., frame-by-frame, can be considered to improve performance. Also, in multiple multiple-input and multiple-output networks with aggressive frequency reuse, we propose the interference cancellation strategy for the proposed sparsity-embracing MUDs. That first cancels out the interference induced by adjacent networks and then recovers the desired users' information by exploiting the low user activity. In simulation studies for binary phase shift keying modulation, numerical evidences establish the effectiveness of our proposed MUDs exploiting low user activity, as compared with the conventional MUD.